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• How do I debug a crash when I run my garbage-collected app in Rosetta?

  - by Rob Keniger

  I have a Universal app which is targeting 10.5 and which uses garbage collection. I am building for ppc, i386 and x86_64. I don't have access to a physical PowerPC machine so I am trying to use Rosetta to confirm that the PowerPC portion of the app works correctly. However, as soon as the app is launched in Rosetta it immediately crashes with the following crash log: Process: FooApp [91567] Path: /Users/rob/Development/src/FooApp/build/Release 64-bit/FooApp.app/Contents/MacOS/FooApp Identifier: com.companyX.FooApp Version: 0.9 (build d540e05) (2) Code Type: PPC (Translated) Parent Process: launchd [708] Date/Time: 2010-04-09 18:32:23.962 +1000 OS Version: Mac OS X 10.6.3 (10D573) Report Version: 6 Exception Type: EXC_CRASH (SIGTRAP) Exception Codes: 0x0000000000000000, 0x0000000000000000 Crashed Thread: 5 ...snip non-relevant threads... Thread 5 Crashed: 0 libSystem.B.dylib 0x8023656a __pthread_kill + 10 1 libSystem.B.dylib 0x80235e17 pthread_kill + 95 2 com.companyX.FooApp 0xb80bfb30 0xb8000000 + 785200 3 com.companyX.FooApp 0xb80c0037 0xb8000000 + 786487 4 com.companyX.FooApp 0xb80dd8e8 0xb8000000 + 907496 5 com.companyX.FooApp 0xb8145397 spin_lock_wrapper + 1791 6 com.companyX.FooApp 0xb801ceb7 0xb8000000 + 118455 I have used the Apple docs on debugging translated apps and the information on this page to attach gdb to the app when it's running in Rosetta. The app immediately breaks into the debugger upon launch: Program received signal SIGTRAP, Trace/breakpoint trap. [Switching to thread 15107] 0x9151fdd4 in auto_fatal () (gdb) bt #0 0x9151fdd4 in auto_fatal () #1 0x91536d84 in Auto::Thread::get_register_state () #2 0x915372f8 in Auto::Thread::scan_other_thread () #3 0x91529be4 in Auto::Zone::scan_registered_threads () #4 0x91539114 in Auto::MemoryScanner::scan_thread_ranges () #5 0x9153b000 in Auto::MemoryScanner::scan () #6 0x9153049c in Auto::Zone::collect () #7 0x915198f4 in auto_collect_internal () #8 0x9151a094 in auto_collection_work () #9 0x96687434 in _dispatch_call_block_and_release () #10 0x9668912c in _dispatch_queue_drain () #11 0x96689350 in _dispatch_queue_invoke () #12 0x966895c0 in _dispatch_worker_thread2 () #13 0x966896fc in _dispatch_worker_thread () #14 0x965a97e8 in _pthread_body () (gdb) I have no idea where to start with this. It looks like the Garbage Collector is failing very badly. Are garbage-collected PowerPC apps not supported in Rosetta? I can't see any mention of this limitation in the docs if so. Does anyone have any ideas?

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• sproutcore vs javascriptMVC for web app development

  - by swami

  Hi, I want to use a javascript framework with MVC for a complex web application (which will be one of a set of related apps and pages) for an intranet in a digital archives. I have been looking at SproutCore and JavascriptMVC. I want to choose one framework and stick with it. Does anybody know what the distinguishing features are when comparing these two? I want something that is simple, straightforward that I can customize/hack easily, and that doesn't get in my way too much, but that at the same time gives me a basis for keeping my code nicely organized, and event-driven. I also plan on using jquery substantially. I know sproutcore is backed by Apple, and looks like it is getting more popular by the day, and it has a nice green website :), whereas JavascriptMVC looks less professional, with less of a following and less momentum behind it. I've done the tutorials for both and I was impressed by SproutCore more (in the JMVC tutorial you don't really do anything substantial) - but somewhere in the back of my mind I feel that JMVC might just be better because it doesn't try and do too much - it just gives you MVC functionality based on a couple of jquery plugins, and you can use jquery for everything else, so its flexible. Whereas SproutCore seems to have more of its own API etc... which is also nice in a way... but then you're kind of stuck within that.... hmmm I'm confused :). Any thoughts would be much appreciated.

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• 3x3 Sobel operator and gradient features

  - by pithyless

  Reading a paper, I'm having difficulty understanding the algorithm described: Given a black and white digital image of a handwriting sample, cut out a single character to analyze. Since this can be any size, the algorithm needs to take this into account (if it will be easier, we can assume the size is 2^n x 2^m). Now, the description states given this image we will convert it to a 512-bit feature (a 512-bit hash) as follows: (192 bits) computes the gradient of the image by convolving it with a 3x3 Sobel operator. The direction of the gradient at every edge is quantized to 12 directions. (192 bits) The structural feature generator takes the gradient map and looks in a neighborhood for certain combinations of gradient values. (used to compute 8 distinct features that represent lines and corners in the image) (128 bits) Concavity generator uses an 8-point star operator to find coarse concavities in 4 directions, holes, and lagrge-scale strokes. The image feature maps are normalized with a 4x4 grid. I'm for now struggling with how to take an arbitrary image, split into 16 sections, and using a 3x3 Sobel operator to come up with 12 bits for each section. (But if you have some insight into the other parts, feel free to comment :)

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• EXC_BAD_ACCESS NSUrlConnection

  - by Lars

  Hi all, i got an EXC_BAD_ACCESS when i perform the last line of the function (webData). -(void)requestSoap{ NSString *requestUrl = @"http://www.website.com/webservice.php"; NSString *soapMessage = @"the soap message"; //website and soapmessage are valid in original code. NSError **error; NSURLResponse *response; //Convert parameter string to url NSURL *url = [NSURL URLWithString:requestUrl]; NSMutableURLRequest *theRequest = [NSMutableURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:10]; NSString *msgLength = [NSString stringWithFormat:@"%d", [soapMessage length]]; //Create an XML message for webservice [theRequest addValue: @"text/xml; charset=utf-8" forHTTPHeaderField:@"Content-Type"]; [theRequest addValue: msgLength forHTTPHeaderField:@"Content-Length"]; [theRequest setHTTPMethod:@"POST"]; [theRequest setHTTPBody: [soapMessage dataUsingEncoding:NSUTF8StringEncoding]]; NSData *webData = [NSURLConnection sendSynchronousRequest:theRequest returningResponse:&response error:error]; } I tried not to release a thing, because what i read on the net is it's almost always a memory thing. When i debug the code (NSZombieEnabled = YES) this is what i get: [Session started at 2010-05-31 15:56:13 +0200.] GNU gdb 6.3.50-20050815 (Apple version gdb-1461.2) (Fri Mar 5 04:43:10 UTC 2010) Copyright 2004 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "x86_64-apple-darwin".sharedlibrary apply-load-rules all Attaching to process 19856. test(19856) malloc: recording malloc stacks to disk using standard recorder test(19856) malloc: enabling scribbling to detect mods to free blocks test(19856) malloc: process 19832 no longer exists, stack logs deleted from /tmp/stack-logs.19832.test.w9Ek4L.index test(19856) malloc: stack logs being written into /tmp/stack-logs.19856.test.URRpQF.index Program received signal: “EXC_BAD_ACCESS”. Does anybody have a clue?? Thanks a lot! Lars

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• How would the conversion of a custom CMS using a text-file-based database to Drupal be tackled?

  - by James Morris

  Just today I've started using Drupal for a site I'm designing/developing. For my own site http://jwm-art.net I wrote a user-unfriendly CMS in PHP. My brief experience with Drupal is making me want to convert from the CMS I wrote. A CMS whose sole method (other than comments) of automatically publishing content is by logging in via SSH and using NANO to create a plain text file in a format like so*: head<<END_HEAD title = Audio keywords= open,source,audio,sequencing,sampling,synthesis descr = Music, noise, and audio, created by James W. Morris. parent = home END_HEAD main<<END_MAIN text<<END_TEXT Digital music, noise, and audio made exclusively with @=xlink=http://www.linux-sound.org@:Linux Audio Software@_=@. END_TEXT image=gfb@--@;Accompanying image for penonpaper-c@right ilink=audio_2008 br= ilink=audio_2007 br= ilink=audio_2006 END_MAIN info=text<<END_TEXT I've been making PC based music since the early nineties - fortunately most of it only exists as tape recordings. END_TEXT ( http://jwm-art.net/dark.php?p=audio - There's just over 400 pages on there. ) *The jounal-entry form which takes some of the work out of it, has mysteriously broken. And it still required SSH access to copy the file to the main dat dir and to check I had actually remembered the format correctly and the code hadn't mis-formatted anything (which it always does). I don't want to drop all the old content (just some), but how much work would be involved in converting it, factoring into account I've been using Drupal for a day, have not written any PHP for a couple of years, and have zero knowledge of SQL? How might a team of developers tackle this? How do-able is it for one guy in his spare time?

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• How can I use Qt to get html code of the redirected page??

  - by Claire Huang

  I'm trying to use Qt to download the html code from the following url: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=nucleotide&cmd=search&term=AB100362 this url will re-direct to www.ncbi.nlm.nih.gov/nuccore/27884304 I try to do it by following way, but I cannot get anything. it works for some webpage such as www.google.com, but not for this NCBI page. is there any way to get this page?? QNetworkReply::NetworkError downloadURL(const QUrl &url, QByteArray &data) { QNetworkAccessManager manager; QNetworkRequest request(url); QNetworkReply *reply = manager.get(request); QEventLoop loop; QObject::connect(reply, SIGNAL(finished()), &loop, SLOT(quit())); loop.exec(); if (reply->error() != QNetworkReply::NoError) { return reply->error(); } data = reply->readAll(); delete reply; return QNetworkReply::NoError; } void GetGi() { int pos; QString sGetFromURL = "http://www.ncbi.nlm.nih.gov/entrez/query.fcgi"; QUrl url(sGetFromURL); url.addQueryItem("db", "nucleotide"); url.addQueryItem("cmd", "search"); url.addQueryItem("term", "AB100362"); QByteArray InfoNCBI; int errorCode = downloadURL(url, InfoNCBI); if (errorCode != 0 ) { QMessageBox::about(0,tr("Internet Error "), tr("Internet Error %1: Failed to connect to NCBI.\t\nPlease check your internect connection.").arg(errorCode)); return "ERROR"; } }

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• Debugging SIGABRT within NSManagedObjectContext -save:

  - by westsider

  From inside NSManagedObjectContext -save: I am getting this message: Assertion failed: (_Unwind_SjLj_Resume() can't return), function _Unwind_SjLj_Resume, file /SourceCache/libunwind/libunwind-24.1/src/Unwind-sjlj.c, line 326. Program received signal: “SIGABRT”. warning: Unable to read symbols for /Developer/Platforms/iPhoneOS.platform/DeviceSupport/4.2.1 (8C148)/Symbols/Developer/usr/lib/libXcodeDebuggerSupport.dylib (file not found). This happens when I delete an Experiment object with to-many with Run which has to-many with Sample which has to-one with Data. Experiment also has to-many with Page which has to-many with Display which has to-many to Run. I mention this to point out the cyclical nature of the graph. Here is a simplified graph of model: I had been using Delete Rules but have now switched to "No Action" delete rules in combination with -prepareForDeletion methods for all of these classes. This change made no difference. In both cases, the error message is the same. Interestingly, when I relaunch the app, all the objects that were marked for deletion have been deleted. Also, if an Experiment has no Run objects, then deletion works without incidence. For that matter, deleting a single Run from an Experiment also works. I am hoping that someone has seen something like this and can offer advice on what would cause this. Or, if someone has advice on how to get libXcodeDebuggerSupport.dylib for iOS 4.2.1, that might also be helpful. Update: I followed advice found here and was able to get Xcode to find libXcodeDebuggerSupport.dylib for iOS 4.2.1. But this did not help at all in diagnosing problem - which persists.

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• how to load multiple images in iCarousel using this code?

  - by Dany

  i'm loading bunch of images in coverflow using i carousel but i'm not getting it?..initially i got Signal sigabart issue..after i edited some of the code the view gets displayed...Am i missing something?... #import "CollectionViewController.h" @interface CollectionViewController () @property (nonatomic, retain) NSMutableArray *items; @end @implementation CollectionViewController @synthesize carousel; @synthesize items; - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil { self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]; if (self) { // Custom initialization } return self; } - (void)dealloc { carousel.delegate = nil; carousel.dataSource = nil; [items release]; [carousel release]; [super dealloc]; } - (void)viewDidLoad { [super viewDidLoad]; carousel.type = iCarouselTypeCoverFlow2; } - (void)viewDidUnload { [super viewDidUnload]; self.carousel = nil; } - (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation { return (interfaceOrientation == UIInterfaceOrientationPortrait); } #pragma mark - #pragma mark iCarousel methods - (NSUInteger)numberOfItemsInCarousel:(iCarousel *)carousel { return [items count]; } - (NSUInteger)numberOfVisibleItemsInCarousel:(iCarousel *)carousel { return 29; } - (UIView *)carousel:(iCarousel *)carousel viewForItemAtIndex:(NSUInteger)index reusingView:(UIView *)view { //create new view if no view is available for recycling if (view == nil) { view = [NSArray arrayWithObjects:[UIImage imageNamed:@"gal1.jpg"], [UIImage imageNamed:@"gal2.jpg"], [UIImage imageNamed:@"gal3.jpg"], [UIImage imageNamed:@"gal5.jpg"], [UIImage imageNamed:@"gal6.jpg"], [UIImage imageNamed:@"gal7.jpg"], [UIImage imageNamed:@"gal8.jpg"], [UIImage imageNamed:@"gal9.jpg"], [UIImage imageNamed:@"gal10.jpg"], [UIImage imageNamed:@"gal11.jpg"], [UIImage imageNamed:@"gal12.jpg"], [UIImage imageNamed:@"gal13.jpg"], [UIImage imageNamed:@"gal14.jpg"], [UIImage imageNamed:@"gal15.jpg"], [UIImage imageNamed:@"gal16.jpg"], [UIImage imageNamed:@"gal17.jpg"], [UIImage imageNamed:@"gal18.jpg"], [UIImage imageNamed:@"gal19.jpg"], [UIImage imageNamed:@"gal20.jpg"], [UIImage imageNamed:@"gal21.jpg"], [UIImage imageNamed:@"gal22.jpg"], [UIImage imageNamed:@"gal23.jpg"], [UIImage imageNamed:@"gal24.jpg"], [UIImage imageNamed:@"gal25.jpg"], [UIImage imageNamed:@"gal26.jpg"], [UIImage imageNamed:@"gal27.jpg"], [UIImage imageNamed:@"gal28.jpg"], } else { } return view; } @end while running on simulator i just get the screen not images?...i got stuck here....

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• Is there any special tool for interactive GUI development

  - by niko

  Hi, Currently I am preparing exercises about networks and mobile communications for students. I was thinking about creating an interactive user-interface which enables the user to drag&drop predefined elements and then implement a logic based upon element distances etc. An example would be to place two base stations (a predefined element with several properties), set the scale in the interface and then check the signal interferrence in the environment (user-interface). The first part might be too abstract whereas the example might be too specific, but I was wondering whether there already exists any friendly framework or language which enables developers to create interactive interfaces (for teaching/learning purpouses) in short ammount of time. Usually I write applications for PC environment in .NET but in this case it would take too much time to create a specific interface for every exercise. I would appreciate if anyone could suggest any way to create interactive user-interface in short ammount of time. Are there any special programming languages or development tools for this kind of applications or are there any useful frameworks for .NET, Java or any other language to speed up the development of user-interfaces? Thank you!

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• iPhone - Failed to save the videos metadata to the filesystem.

  - by cameron

  My application uses the UIImagePicker to allow the user to use the camera and capture a photo to edit/etc. I am getting the error message below: 2010-02-03 10:41:24.018 LivingRoom[5333:5303] Failed to save the videos metadata to the filesystem. Maybe the information did not conform to a plist. Program received signal: “EXC_BAD_ACCESS”. A search in Google brings up a number of threads in various forums, with no ultimate response/root cause/suggestions on how to fix/debug. An example is the thread below with code which is very similar to my app: http://groups.google.com/group/iphonesdkdevelopment/browse_thread/thread/6b7b396c62bef398 The error disappears for a while (10 tests in a row, no errors) if I reboot the iPhone. I have not been able to determine what makes it reoccur after a reboot, but it does. I am not using the video source and the fact that a reboot solves the problem for a while points to some sort of mem leak (perhaps?). The problem always shows up on both the iPhone (even after the reboot) and the simulator when choosing a photo from the album, but the app does not crash on the iPhone or the simulator. The same app with exact code did not have the error message when compiled using SDK 3.0 (last August/September). But 3.1.x has always produced the error message, which means that once a week or so the iPhone needs to be rebooted for the error to disappear. The users are not happy with that solution any longer!! Any suggestion/clues would be greatly appreciated.

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• Problems with QDialog in Qt

  - by Martin

  I'm using Qt for Symbian. I have some problems with a QDialog that I open from a QMenu. The QDialog shows up fine and in the QDialog I have a QDialogButtonBox with a button to Close the QDialog. BUT if I close the QDialog and then open it from the QMenu again, it will show up but the button from the QDialogButtonBox will not show up. Instead the buttons from the QMainWindow will show but they are grayed out. How can I get the QDialog buttons to show every time? Maybe I have some problems with setting focus on the QDialog? I really can't see what I'm doing wrong here. It's not much code that I use, you can try it yourself. This is my code: In QMainWindow I use the following to create the menu: QAction *menuButton = new QAction("Menu", this); menuButton->setSoftKeyRole(QAction::PositiveSoftKey); QMenu *menu = new QMenu(this); menuButton->setMenu(menu); QAction *popup = new QAction("Show popup",this); connect(popup, SIGNAL(triggered()), this, SLOT(showPopup())); menu->addAction(popup); addAction(menuButton); This shows the QDialog: void MyMainWindow::showPopup(){ TestDialog *test = new TestDialog(this); test->setAttribute(Qt::WA_DeleteOnClose); test->show(); } This is the TestDialog: TestDialog::TestDialog(QWidget *parent) : QDialog(parent) { ui.setupUi(this); QDesktopWidget* desktopWidget = QApplication::desktop(); QRect rect = desktopWidget->availableGeometry(); this->setFixedWidth(rect.width()); }

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• How to exploit Diffie-hellman to perform a man in the middle attack

  - by jfisk

  Im doing a project where Alice and Bob send each other messages using the Diffie-Hellman key-exchange. What is throwing me for a loop is how to incorporate the certificate they are using in this so i can obtain their secret messages. From what I understand about MIM attakcs, the MIM acts as an imposter as seen on this diagram: Below are the details for my project. I understand that they both have g and p agreed upon before communicating, but how would I be able to implement this with they both having a certificate to verify their signatures? Alice prepares ?signA(NA, Bob), pkA, certA? where signA is the digital signature algorithm used by Alice, “Bob” is Bob’s name, pkA is the public-key of Alice which equals gx mod p encoded according to X.509 for a fixed g, p as specified in the Diffie-Hellman key- exchange and certA is the certificate of Alice that contains Alice’s public-key that verifies the signature; Finally, NA is a nonce (random string) that is 8 bytes long. Bob checks Alice's signature, and response with ?signB{NA,NB,Alice},pkB,certB?. Alice gets the message she checks her nonce NA and calculates the joint key based on pkA, pkB according to the Diffie-Hellman key exchange. Then Alice submits the message ?signA{NA,NB,Bob},EK(MA),certA? to Bob and Bobrespondswith?SignB{NA,NB,Alice},EK(MB),certB?. where MA and MB are their corresponding secret messages.

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• Reference for proper handling of PID file on Unix

  - by bignose

  Where can I find a well-respected reference that details the proper handling of PID files on Unix? On Unix operating systems, it is common practice to “lock” a program (often a daemon) by use of a special lock file: the PID file. This is a file in a predictable location, often ‘/var/run/foo.pid’. The program is supposed to check when it starts up whether the PID file exists and, if the file does exist, exit with an error. So it's a kind of advisory, collaborative locking mechanism. The file contains a single line of text, being the numeric process ID (hence the name “PID file”) of the process that currently holds the lock; this allows an easy way to automate sending a signal to the process that holds the lock. What I can't find is a good reference on expected or “best practice” behaviour for handling PID files. There are various nuances: how to actually lock the file (don't bother? use the kernel? what about platform incompatibilities?), handling stale locks (silently delete them? when to check?), when exactly to acquire and release the lock, and so forth. Where can I find a respected, most-authoritative reference (ideally on the level of W. Richard Stevens) for this small topic?

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• Mathematical annotations in a PDF file

  - by kvaruni

  I like to annotate papers I read in a digital way. Numerous programs exist to help in this process. For example, on OS X one can use programs such as Skim or even Preview. However, making annotations is dreadful when one wishes to add mathematical annotations, such as formulas or greek letters. A cumbersome "solution" is to select the desired symbol one by one using the Special Characters palette, though this considerably slows down the annotation process. Is there any way to add mathematical annotations to a PDF? The only two limitations that I would impose on a solution is that 1) the mathematical text needs to be selectable, i.e. it must be text and 2) I want to limit the number of programs I need to make the process as painless as possible. Some of the more promising solutions I have tried include generating LaTeX with LaTeXiT, but it seems to be impossible to add a PDF on top of another PDF. Another attempt was to use jsMath to generate the symbols and copy-paste these as annotation using one of the jsMath fonts. This results in unreadable, incorrect characters.

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• STLport crash (race condition, Darwin only?)

  - by Jonas Byström

  When I run STLport on Darwin I get a strange crash. (Haven't seen it anywhere else than on Mac, but exactly same thing crash on both i686 and PowerPC.) This is what it looks like in gdb: Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: 13 at address: 0x0000000000000000 [Switching to process 21097] 0x000000010120f47c in stlp_std::__node_alloc_impl::_M_allocate () It may be some setting in STLport, I noticed that Mac.h and MacOSX.h seemed far behind on features. I also know that it it must be some type of race condition, since it doesn't occur just by calling this method (implicity called). The crash happens mainly when I push the system, running 10 simultaneous threads that do a lot of string handling. Other theories I come up with have to do with compiler flags (configure script) and g++ 4.2 bugs (seems like 4.4.3 isn't on Mac yet with Objective-C support, which I need to link with). HELP!!! :) Edit: I run unit tests, which do all sorts of things. This problem arise when I start 10 threads that push the system; and it always comes down to std::string::append which eventually boils down to _M_allocate. Since I can't even get a descent dump of the code that's causing the problem, I figure I'm doing something bad. Could it be so since it's trying to execute at instruction pointer 0x000...000? Are dynlibs built as DLLs in Windows with a jump table? Could it perhaps be that such a jump table has been overwritten for some reason? That would probably explain this behavior. (The code is huge, if I run out of other ideas, I'll post a minimum crashing sample here.)

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• pthread windows event equivalent question

  - by ScaryAardvark

  I have the following code which replicates the windows manual and auto reset events. class event { public: event( bool signalled = false, bool ar = true ) : _auto( ar ), _signalled( signalled ) { pthread_mutex_init( &_mutex, NULL ); pthread_cond_init( &_cond, NULL ); } ~event() { pthread_cond_destroy( &_cond ); pthread_mutex_destroy( &_mutex ); } void set() { pthread_mutex_lock( &_mutex ); // only set and signal if we are unset if ( _signalled == false ) { _signalled = true; pthread_cond_signal( &_cond ); } pthread_mutex_unlock( &_mutex ); } void wait() { pthread_mutex_lock( &_mutex ); while ( _signalled == false ) { pthread_cond_wait( &_cond, &_mutex ); } // if we're an autoreset event, auto reset if ( _auto ) { _signalled = false; } pthread_mutex_unlock( &_mutex ); } void reset() { pthread_mutex_lock( &_mutex ); _signalled = false; pthread_mutex_unlock( &_mutex ); } private: pthread_mutex_t _mutex; pthread_cond_t _cond; bool _signalled; bool _auto; }; My question surrounds the "optimisation" I've put in place in the set() method where I only call pthread_cond_signal() if the event was unsignalled. Is this a valid optimisation or have I introduced some subtle flaw by doing so.

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• Anyone got a nifty credit expiry algorithm?

  - by garethkeenan

  Our website uses a credit system to allow users to purchase inexpensive digital goods (eg. photos). We use credits, rather than asking the user to pay for items individually, because the items are cheap and we are trying to keep our credit-card/PayPal overhead low. Because we aren't a bank, we have to expire credits after a certain amount of time. We expire deposit credits after a year, but other types of credits (bonuses, prizes, refunds) may have a different shelf-life. When a buyer buys an item, we spend the credit that is going to expire first. Our current system keeps track of every deposit by storing the original value and the remainder to be spent. We keep a list of all purchases as well, of course. I am currently moving to a system which is much more like a traditional double-entry accounting system. A deposit will create a ledger item, increasing the user's 'spending' account balance. Every purchase will also create a ledger item, decreasing the user's 'spending' account balance. The new system has running balances, while the old system does not, which greatly improves our ability to find problems and do reconciliations. We do not want to use the old system of keeping a 'remainder' value attached to each deposit record because it is inefficient to replay a user's activities to calculate what the remainder of each deposit is over time (for the user's statement). So, after all of this verbose introduction, my question is "Does anyone else out there have a similar system of expiring credits?" If you could describe how you calculate expired credits it would be a great help. If all expired credits had the exact same shelf life, we would be able to calculate the expired amount using: Total Deposits - Total Spending - Deposits Not Due To Expire = Amount to Expire However, because deposits can have different shelf lives, this formula does not work because more than one deposit can be partially spent at any given time.

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• Sync Vs. Async Sockets Performance in .NET

  - by Michael Covelli

  Everything that I read about sockets in .NET says that the asynchronous pattern gives better performance (especially with the new SocketAsyncEventArgs which saves on the allocation). I think this makes sense if we're talking about a server with many client connections where its not possible to allocate one thread per connection. Then I can see the advantage of using the ThreadPool threads and getting async callbacks on them. But in my app, I'm the client and I just need to listen to one server sending market tick data over one tcp connection. Right now, I create a single thread, set the priority to Highest, and call Socket.Receive() with it. My thread blocks on this call and wakes up once new data arrives. If I were to switch this to an async pattern so that I get a callback when there's new data, I see two issues The threadpool threads will have default priority so it seems they will be strictly worse than my own thread which has Highest priority. I'll still have to send everything through a single thread at some point. Say that I get N callbacks at almost the same time on N different threadpool threads notifying me that there's new data. The N byte arrays that they deliver can't be processed on the threadpool threads because there's no guarantee that they represent N unique market data messages because TCP is stream based. I'll have to lock and put the bytes into an array anyway and signal some other thread that can process what's in the array. So I'm not sure what having N threadpool threads is buying me. Am I thinking about this wrong? Is there a reason to use the Async patter in my specific case of one client connected to one server?

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• Qt QFileDialog - native dialogs only with static functions?

  - by darron

  I'm trying to simply save a file. However, I need a filename entered without a suffix to automatically get a default suffix (which setDefaultSuffix() does). I'd rather not completely lose the native save dialog just for this. exec() is not overloaded from QDialog, so it totally bypasses the native hook (ignoring the DontUseNativeDialog option even if it's false). If I disable the file overwrite warning and append the default suffix myself after the function returns, then I'd be re-opening the dialog if the user did not want to overwrite... and that's just ugly. Is there some signal I can catch and quickly inject the default suffix if it's not there? I'm guessing not, since it's a native dialog. Is there something I'm doing wrong with the filter? I only have one filter choice. It should use that extension. This seems pretty lame. Launching the save dialog and simply typing "test" should never result in an extensionless file. "test.", yes. "test" no way. That'll really confuse the users when they hit Load and can't see the file they just saved. I guess the cross-platform part of Qt is giving me lowest common denominator file dialog functionality?

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• How to make a model instance read-only after saving it once?

  - by Ryszard Szopa

  One of the functionalities in a Django project I am writing is sending a newsletter. I have a model, Newsletter and a function, send_newsletter, which I have registered to listen to Newsletter's post_save signal. When the newsletter object is saved via the admin interface, send_newsletter checks if created is True, and if yes it actually sends the mail. However, it doesn't make much sense to edit a newsletter that has already been sent, for the obvious reasons. Is there a way of making the Newsletter object read-only once it has been saved? Edit: I know I can override the save method of the object to raise an error or do nothin if the object existed. However, I don't see the point of doing that. As for the former, I don't know where to catch that error and how to communicate the user the fact that the object wasn't saved. As for the latter, giving the user false feedback (the admin interface saying that the save succeded) doesn't seem like a Good Thing. What I really want is allow the user to use the Admin interface to write the newsletter and send it, and then browse the newsletters that have already been sent. I would like the admin interface to show the data for sent newsletters in an non-editable input box, without the "Save" button. Alternatively I would like the "Save" button to be inactive.

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• Debugging NSoperation BAD ACCESS within graphics context

  - by Joe

  I tried everything to debug this one but I can't get to the bottom of it. This code lives in a subclass of NSOperation which is processed from a queue: (borders is an ivar NSArray containing 5 UIimage objects) NSMutableArray *images = [[NSMutableArray alloc] init]; for (unsigned i = 0; i < 5; i++) { CGSize size = CGSizeMake(60, 60); UIGraphicsBeginImageContext(size); CGPoint thumbPoint = CGPointMake(6, 6); [controller.image drawAtPoint:thumbPoint]; CGPoint borderPoint = CGPointMake(0, 0); [[borders objectAtIndex:i] drawAtPoint:borderPoint]; [images addObject:UIGraphicsGetImageFromCurrentImageContext()]; UIGraphicsEndImageContext(); } [images release]; The code works fine most of the time but when I push the iphone by access subviews and pressing lots of buttons on the UI I either get this exception which is trapped by the operation: Exception Load view: *** -[NSCFArray insertObject:atIndex:]: attempt to insert nil or I get this: Program received signal: “EXC_BAD_ACCESS”. The exception is caused because UIGraphicsGetImageFromCurrentImageContext() return nil. I don't know how to debug the EXC_BAD_ACCESS but I'm guessing that this error (in fact both of these errors) is caused by low memory. The debugger stops at the line: [controller.image drawAtPoint:thumbPoint]; As I mentioned I've trapped the exception so I can live with that but the EXC_BAD_ACCESS is more serious. IF this is memory related how can I tell and is it possible to increase the memory available to NSOperation?

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• System.Dynamic bug?

  - by ControlFlow

  While I playing with the C# 4.0 dynamic, I found strange things happening with the code like this: using System.Dynamic; sealed class Foo : DynamicObject { public override bool TryInvoke( InvokeBinder binder, object[] args, out object result) { result = new object(); return true; } static void Main() { dynamic foo = new Foo(); var t1 = foo(0); var t2 = foo(0); var t3 = foo(0); var t4 = foo(0); var t5 = foo(0); } } Ok, it works but... take a look at IntelliTrace window: So every invokation (and other operations too on dynamic object) causes throwing and catching strange exceptions twice! I understand, that sometimes exceptions mechanism may be used for optimizations, for example first call to dynamic may be performed to some stub delegate, that simply throws exception - this may be like a signal to dynamic binder to resolve an correct member and re-point delegate. Next call to the same delegate will be performed without any checks. But... behavior of the code above looks very strange. Maybe throwing and catching exceptions twice per any operation on DynamicObject - is a bug?

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• Dynamically created iframe used to download file triggers onload with firebug but not without

  - by justkt

  EDIT: as this problem is now "solved" to the point of working, I am looking to have the information on why. For the fix, see my comment below. I have an web application which repeatedly downloads wav files dynamically (after a timeout or as instructed by the user) into an iframe in order to trigger the a default audio player to play them. The application targets only FF 2 or 3. In order to determine when the file is downloaded completely, I am hoping to use the window.onload handler for the iframe. Based on this stackoverflow.com answer I am creating a new iframe each time. As long as firebug is enabled on the browser using the application, everything works great. Without firebug, the onload never fires. The version of firebug is 1.3.1, while I've tested Firefox 2.0.0.19 and 3.0.7. Any ideas how I can get the onload from the iframe to reliably trigger when the wav file has downloaded? Or is there another way to signal the completion of the download? Here's the pertinent code: HTML (hidden's only attribute is display:none;): <div id="audioContainer" class="hidden"> </div> JavaScript (could also use jQuery, but innerHTML is faster than html() from what I've read): waitingForFile = true; // (declared at the beginning of closure) $("#loading").removeClass("hidden"); var content = "<iframe id='audioPlayer' name='audioPlayer' src='" + /path/to/file.wav + "' onload='notifyLoaded()'></iframe>"; document.getElementById("audioContainer").innerHTML = content; And the content of notifyLoaded: function notifyLoaded() { waitingForFile = false; // (declared at beginning of the closure) $("#loading").addClass("hidden"); } I have also tried creating the iframe via document.createElement, but I found the same behavior. The onload triggered each time with firebug enabled and never without it. EDIT: Fixed the information on how the iframe is being declared and added the callback function code. No, no console.log calls here.

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• DOS batch file to enter commands in proprietary java app and receive feedback?

  - by Justine

  Hello, I'm working on a project in which I'd like to be able to turn lights on and off in the Duke Smart Home via a high frequency chirp. The lighting system is called Clipsal Square-D and the program that gives a user access to the lighting controls is called CGate. I was planning on doing some signal processing in Matlab, then create a batch file from Matlab to interact with Cgate. Cgate is a proprietary Java app that, if run from a DOS command line, opens up another window that looks like the command prompt. I have a batch file that can check to see if Cgate is running and if not, open it. But what I can't figure out how to do is actually run commands in the Cgate program from the batch file and likewise, take the response from Cgate. An example of such a command is "noop," which should return "200 OK." Any help would be much appreciated! Thank you very much in advance :) (here's my existing batch file by the way) @ECHO off goto checkIfOpen :checkIfOpen REM pv finds all open processes and puts it in result.txt %SystemRoot%\pv\pv.exe %SystemRoot%\pv\pv.exe result.txt REM if result has the word notepad in it then notepad is running REM if not then it opens notepad FIND "notepad.exe" result.txt IF ERRORLEVEL 1 START %SystemRoot%\system32\Clipsal\C-Gate2\cgate.exe goto end :end

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• Push different views from a table.

  - by Tanner

  Hello All, Ive been following a tutorial to implement a search bar ( http://www.iphonesdkarticles.com/2009/01/uitableview-searching-table-view.html ) However I cant seem to push different views. Here is what my didsSelectRowAtIndexPath looks like. - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { NSString *selectedCountry = nil; if(searching) selectedCountry = [copyListOfItems objectAtIndex:indexPath.row]; else { NSDictionary *dictionary = [listOfItems objectAtIndex:indexPath.section]; NSArray *array = [dictionary objectForKey:@"Countries"]; selectedCountry = [array objectAtIndex:indexPath.row]; } //Initialize the detail view controller and display it. if ([[listOfItems objectAtIndex:indexPath.row] isEqual:@"neon"]){ Neon *abo = [[Neon alloc] initWithNibName:@"Neon" bundle:nil]; //dvController.selectedCountry = selectedCountry; [self.navigationController pushViewController:abo animated:YES]; [abo release]; } } And here is the debuger message when I click on neon: 2010-05-09 08:47:27.516 iTeachU[3821:307] * Terminating app due to uncaught exception 'NSRangeException', reason: ' -[NSMutableArray objectAtIndex:]: index 60 beyond bounds [0 .. 0]' ** Call stack at first throw: terminate called after throwing an instance of 'NSException' Program received signal: “SIGABRT”. If anyone has a way to push views based on the cells text it would be greatly appreciated. Thanks

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